I don't want to discourage you, but converting a driver to be slot based is a lot of work and usually means rewriting it. A few examples from me are here:

https://git.redump.net/mame/commit/?id=09f25df20d7910b6f156c86040f9a9ca35852701
https://git.redump.net/mame/commit/?id=4d89de93c0dcb0b3069c9226236bfb1a802113cf

This isn't the only way to do it, there are different ways to implement a slot based system. Just look at a few examples in src/devices/bus.